Optical, incident-light position measuring devices usually include a material measure as well as a scanning unit that is movable relatively thereto. Typically arranged at the scanning unit is a light source, which emits a light bundle in the direction of the material measure. From there, the light bundle is reflected back in the direction of the scanning unit, where the light bundle, which is modulated in dependence upon displacement, passes through, as the case may be, one or more graduated-scale scanning structures, and is ultimately measured by an opto-electronic detector system. The signals generated in this manner and modulated in dependence upon displacement are then further processed via a downstream evaluation unit.
Conventional material measures include a substrate material on which alternating subsections having different optical characteristics are arranged. In the case of incident light, the first and second subsections having different reflection characteristics alternate. In the case of an incremental graduation, the configuration of the various subsections extend in the measuring direction. For example, it may be provided to produce subsections of high and low reflectivity on a glass substrate. Alternatively, steel is also used as a substrate material, on which subsections having high and low reflectivity are likewise formed. In this connection, the subsections of high reflectivity may be made of gold, while in the subsections of lower reflectivity, the steel surface is etched to be dull, so that the light impinging there is absorbed or diffusely reflected.
Problems result in the case of the above-described position measuring devices from the influence of scattered light, i.e., from radiation that travels directly from the light source to the detector elements without being modulated by the appropriate material measure. The modulation degree of the scanning signals is reduced by such scattered light.
Such problems are able to be at least partially avoided by using a material measure having photoluminescent subsections as described in German Published Patent Application No. 1 227 246, for example. Radiation having the respective photoluminescence wavelength reaches the detector elements in this context. However, the excitation wavelength differs from this radiation and does not further influence the position determination. However, the foregoing does not provide any further information regarding the concrete development of the material measure, in particular the development of the photoluminescent subsections. Furthermore, it is not yet reliably ensured that no scattered light from the light source reaches the detector elements.